java - 你如何使用消息类中的 what 字段？

Question

有人可以向我解释如何使用 switch 和 what 字段来确定要执行的代码。此外，如何创建要在开关中使用的消息对象也很棒。

我的处理程序代码示例:

Handler uiHandler = new Handler(){
    public void handleMessage(Message msg){
        switch(msg.what){

        }
    }
};

Answer 1

如果您正在使用处理程序，我假设您想在不同的线程中做一些工作，并且正在使用处理程序与您正在启动的线程和主线程进行 b/w 通信。举个例子:

private static final int SUCCESS = 0;
private static final int FAIL = 1;

//This is the handler
Handler uiHandler = new Handler(){
    @Override
    public void handleMessage(Message msg){
        //Here is how you use switch statement
        switch(msg.what){
        case SUCCESS:
            //Do something      
            break;
        case FAIL:
            //Do something
            break;
        }

    }
};

//Here is an example how you might call it
Thread t = new Thread() {
    @Override
    public void run(){
        doSomeWork();
        if(succeed){
            /*we can't update the UI from here so we'll signal our handler 
             and it will do it for us.*/
            // 'sendEmptyMessage(what)' sends a Message containing only the 'what' value.
            uiHandler.sendEmptyMessage(SUCCESS);
        }else{
            uiHandler.sendEmptyMessage(FAIL);
        }
    }   
}

归功于这两个线程:它们可能是一本好书: Android: When should I use a Handler() and when should I use a Thread? & Android Handler actions not being processed

希望这对您有所帮助。